Currently, an optical fiber used for an optical fiber communication system which is generally spreading adopts a structure in which an outer periphery of a core is surrounded by a clad, and an optical signal propagates in this core to transmit information. Further, as the optical communication system spreads in recent years, the amount of information to be transmitted is remarkably increasing. As the amount of information to be transmitted increases, the optical fiber communication system uses several tens to several hundreds of multiple optical fibers to perform long distance optical communication of large capacity.
To reduce the number of optical fibers in such an optical fiber communication system, it is known as disclosed in, for example, following Non-Patent Document 1 that a plurality of signals is transmitted as light propagating in cores using a multicore fiber in which outer peripheries of a plurality of cores are surrounded by a clad.